"He killed those men because he had a delusion. He believed in his mind that they were going to kill him," lawyer Warren St John said in closing arguments.The judge told jurors they could find a person innocent by reason of insanity if the defendant did not know the conduct was wrong due to a severe mental defect or illness.During the trial, jurors heard how Kyle and Littlefield knew something was badly wrong minutes before Routh opened fire.A Texas man has been jailed for life without the possibility of parole after a jury found him guilty of murdering Chris Kyle, the former US Navy SEAL whose autobiography was turned into the hit movie American Sniper.Eddie Ray Routh, 27, a former US Marine, was found guilty of fatally shooting Kyle and Kyle's friend Chad Littlefield multiple times at a gun range about 110 kilometres south-west of Fort Worth in February 2013.Kyle, who helped counsel troubled veterans with trips for shooting and talks, had driven Routh to the range with Kyle's neighbour, Littlefield."You took the lives of two heroes, men that tried to be a friend to you. You became an American disgrace," Littlefield's brother-in-law, Jerry Richardson, said of Routh in court after the sentence was handed down."We have waited two years for God to give us justice on behalf of our son, and God has proved to be faithful," Littlefield's mother Judy said."We are so thrilled that we have the verdict that we have."The jury deliberated for a little more than two hours before reaching a verdict after a two-week trial in the rural Texas city of Stephenville.Prosecutors had been seeking a life sentence without parole.Defence lawyers argued that Routh was a paranoid schizophrenic and should be declared innocent by reason of insanity.In closing arguments, prosecutor Jane Starnes said Routh acted coldly and deliberately when he waited for Kyle to empty his gun at the range and then ambushed the two from behind before fleeing the scene in Kyle's pick-up truck."That is not insanity. That is just cold, calculated capital murder," Ms Starnes said.The trial focused renewed attention on Kyle, who was credited with the most confirmed kills of any US military sniper at 160.Kyle 'never saw it coming'Defence lawyers told the jury that Routh had been to hospitals four times because of his mental illness and was diagnosed as psychotic.They said he was suffering a paranoid episode when he went to the range and met the state's legal definition of insanity. "This dude is straight up nuts," Kyle wrote to Littlefield in an alarmed text message."He's right behind me, watch my six," replied his friend, using military jargon for "watch my back".A forensics expert called by prosecutors said Kyle and Littlefield were shot in the back at close range.They had no time to remove loaded guns that they had holstered."He [Kyle] absolutely never saw this coming," crime scene analyst Howard Ryan said.Prosecutors said the two were shot by 12 or 13 bullets and that Routh put on an act to get out of trouble."He is capable of dreaming up excuses to get his hide out of trouble at convenient times depending on who he is talking to," prosecutor Alan Nash said.Jurors saw police videos where Routh confessed to the killings in a rambling speech and heard audio tape of a prison phone call to a reporter where he talked about shooting Littlefield first, saying he was angry that he came to the range.He allegedly confessed to the killings after complaining that "people were sucking his soul and that he could smell the pigs".